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      函数的递归
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        <p>首先，解释一下什么是递归——程序调用自身的编程技巧称为递归（ recursion）。递归做为一种算法在程序设计语言中广泛应用。递归需要有边界条件、递归前进段和递归返回段。当边界条件不满足时，递归前进；当边界条件满足时，递归返回。<br><a id="more"></a></p>
<p>下面举一个经典的递归函数的例子：<br><figure class="highlight js"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div></pre></td><td class="code"><pre><div class="line"><span class="function"><span class="keyword">function</span> <span class="title">f</span>(<span class="params">n</span>)</span>&#123;</div><div class="line">    <span class="keyword">if</span>(n == <span class="number">0</span> || n == <span class="number">1</span>)&#123;</div><div class="line">        <span class="keyword">return</span> <span class="number">1</span>;</div><div class="line">    &#125;<span class="keyword">else</span>&#123;</div><div class="line">        <span class="keyword">return</span> n*f(n<span class="number">-1</span>);</div><div class="line">    &#125;</div><div class="line">&#125;</div></pre></td></tr></table></figure></p>
<p>那么，根据上面的例子，我们来具体分析一下递归程序的基本步骤：</p>
<ol>
<li>递归就是方法里调用自身。</li>
<li>在使用递增归策略时，必须有一个明确的递归结束条件，称为递归出口。</li>
<li>使用更简单的子问题重新定义答案。我们可以将答案定义为当前节点的内容加上列表中其余部分的和。</li>
<li>合并结果。递归调用之后，我们将当前节点的值加到递归调用的结果上。</li>
</ol>
<p>由于在新项目中的需求，我就想到使用递归函数来实现，问题是这样的：</p>
<blockquote>
<p>给你一个数组，数组的每个元素都是一个对象，需要比较每个元素对象里面的两个属性的值是否相同，如果相同，则合并该元素将里面的count计数属性值相加 </p>
</blockquote>
<p>下面就贴上答案：</p>
<figure class="highlight js"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div><div class="line">20</div><div class="line">21</div><div class="line">22</div><div class="line">23</div><div class="line">24</div><div class="line">25</div><div class="line">26</div><div class="line">27</div><div class="line">28</div><div class="line">29</div><div class="line">30</div><div class="line">31</div><div class="line">32</div><div class="line">33</div><div class="line">34</div><div class="line">35</div><div class="line">36</div><div class="line">37</div><div class="line">38</div><div class="line">39</div><div class="line">40</div><div class="line">41</div><div class="line">42</div><div class="line">43</div><div class="line">44</div><div class="line">45</div><div class="line">46</div><div class="line">47</div><div class="line">48</div><div class="line">49</div><div class="line">50</div><div class="line">51</div><div class="line">52</div><div class="line">53</div><div class="line">54</div><div class="line">55</div><div class="line">56</div><div class="line">57</div><div class="line">58</div><div class="line">59</div><div class="line">60</div><div class="line">61</div><div class="line">62</div><div class="line">63</div><div class="line">64</div><div class="line">65</div><div class="line">66</div><div class="line">67</div><div class="line">68</div><div class="line">69</div></pre></td><td class="code"><pre><div class="line"><span class="comment">/**</span></div><div class="line"><span class="comment"> * uniqueData</span></div><div class="line"><span class="comment"> * arr -&gt; 传入的数组，[注：此数组的每个元素都是一个对象，各元素的属性相同值不同]</span></div><div class="line"><span class="comment"> * field -&gt; 传入比较的属性值，[field是一个数组]</span></div><div class="line"><span class="comment"> * count -&gt; 传递需要处理的属性键，[注；count属性值必须为number，以作统计]</span></div><div class="line"><span class="comment"> * jsonArray -&gt; 存入去重合并后的元素</span></div><div class="line"><span class="comment"> */</span></div><div class="line"></div><div class="line"><span class="keyword">let</span> jsonArray = [];</div><div class="line"><span class="comment">// 去重合并</span></div><div class="line"><span class="keyword">let</span> uniqueData = <span class="function"><span class="keyword">function</span>(<span class="params">arr,field,count</span>)</span>&#123;</div><div class="line">    <span class="keyword">let</span> narr = arr</div><div class="line">    <span class="keyword">if</span>(narr.length &gt; <span class="number">1</span>)&#123;</div><div class="line">        <span class="keyword">let</span> first = narr.shift();</div><div class="line">        <span class="keyword">if</span>(narr.length &gt; <span class="number">0</span>)&#123;</div><div class="line">            <span class="keyword">let</span> next = narr.findIndex(<span class="function">(<span class="params">value,index,array</span>)=&gt;</span>&#123;</div><div class="line">                <span class="keyword">return</span> field.map(<span class="function">(<span class="params">val,index</span>)=&gt;</span>&#123;</div><div class="line">                    <span class="keyword">return</span> first[val] == value[val]</div><div class="line">                &#125;).reduce(<span class="function">(<span class="params">prev,next</span>) =&gt;</span> prev&amp;&amp;next )</div><div class="line">            &#125;)</div><div class="line">            <span class="keyword">if</span>(next &gt;= <span class="number">0</span>)&#123;</div><div class="line">                first[count] += <span class="built_in">parseInt</span>(narr[next][count]);</div><div class="line">                narr.splice(next,<span class="number">1</span>);</div><div class="line">                narr.splice(<span class="number">0</span>,<span class="number">0</span>,first);</div><div class="line">                uniqueData(narr,field,count);</div><div class="line">            &#125;<span class="keyword">else</span>&#123;</div><div class="line">                jsonArray.push(first);</div><div class="line">                uniqueData(narr,field,count);</div><div class="line">            &#125;</div><div class="line">        &#125;<span class="keyword">else</span>&#123;</div><div class="line">            jsonArray.push(first)</div><div class="line">        &#125;</div><div class="line">        </div><div class="line">    &#125;<span class="keyword">else</span>&#123;</div><div class="line">        jsonArray.push(narr[<span class="number">0</span>])</div><div class="line">    &#125;</div><div class="line">&#125;</div><div class="line"></div><div class="line"><span class="comment">// 模拟数据</span></div><div class="line"><span class="keyword">var</span> data = [</div><div class="line">    &#123;</div><div class="line">        count:<span class="number">1</span>,</div><div class="line">        selected:<span class="number">0</span>,</div><div class="line">        subselectd:<span class="number">1</span>,</div><div class="line">        stock:<span class="number">22</span></div><div class="line">    &#125;,&#123;</div><div class="line">        count:<span class="number">2</span>,</div><div class="line">        selected:<span class="number">0</span>,</div><div class="line">        subselected:<span class="number">1</span>,</div><div class="line">        stock:<span class="number">22</span></div><div class="line">    &#125;,&#123;</div><div class="line">        count:<span class="number">1</span>,</div><div class="line">        selected:<span class="number">1</span>,</div><div class="line">        subselected:<span class="number">2</span>,</div><div class="line">        stock:<span class="number">11</span></div><div class="line">    &#125;,&#123;</div><div class="line">        count:<span class="number">3</span>,</div><div class="line">        selected:<span class="number">0</span>,</div><div class="line">        subselected:<span class="number">1</span>,</div><div class="line">        stock:<span class="number">22</span></div><div class="line">    &#125;,&#123;</div><div class="line">        count:<span class="number">1</span>,</div><div class="line">        selected:<span class="number">1</span>,</div><div class="line">        subselected:<span class="number">2</span>,</div><div class="line">        stock:<span class="number">11</span></div><div class="line">    &#125;</div><div class="line">];</div><div class="line">uniqueData(data,[<span class="string">'selected'</span>,<span class="string">'subselected'</span>],<span class="string">'count'</span>);</div><div class="line"><span class="built_in">console</span>.log(jsonArray);</div></pre></td></tr></table></figure>
<p>可能以上的代码不是最好的方案，如果有比较好的方案，请多多指教，谢谢！</p>
<h2 id="总结递归算法解决问题的特点："><a href="#总结递归算法解决问题的特点：" class="headerlink" title="总结递归算法解决问题的特点："></a>总结递归算法解决问题的特点：</h2><ul>
<li>递归就是方法里调用自身。</li>
<li>在使用递增归策略时，必须有一个明确的递归结束条件，称为递归出口。</li>
<li>递归算法解题通常显得很简洁，但递归算法解题的运行效率较低。所以一般不提倡用递归算法设计程序。</li>
<li>在递归调用的过程当中系统为每一层的返回点、局部量等开辟了栈来存储。递归次数过多容易造成栈溢出等，所以一般不提倡用递归算法设计程序。</li>
</ul>

      
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